1. Field of the Invention
The present invention relates to a bending device, and in particular a bending device for a flat rolling mill having four-high or multi-roll stands with working rolls, support rolls and, as applicable, intermediate rolls arranged between the working rolls and the support rolls. The bending device includes bending blocks run vertically in windows of the roll stand so as to act bilaterally on each bearing chuck of the rolls. Piston-cylinder units enable the vertically opposite bending blocks of a roll pair to be movable toward and away from each other.
2. Description of the Related Art
When strip material is rolled in flat rolling mills, high deformation forces are applied to the rolled material and must be absorbed as reaction forces by the roll stands. The roll stands are designed accordingly, but material deformation of the stands as well as the rolls nonetheless occurs. Although the deformation of the working rolls can be reduced by supporting the working rolls with support rolls and, in some cases, intermediate rolls that are arranged between the working rolls and the support rolls, it cannot be prevented. Without countermeasures, the bending of the working rolls toward the side away from the rolled material results in the roll gap taking on a convex cross-sectional shape so that the rolled material is more strongly deformed at the edges than in the middle.
This process can be influenced in various ways, for example, by crowning the rolls, i.e., grinding the roll barrels convexly. This allows the bending of the rolls to be largely compensated for-but only for a certain roll load.
Another common way to compensate for roll bending consists of deliberately bending a roll by use of special bending devices. The deliberate bending is directed counter to the bending that results from the roll force. The special bending devices allow the bending that results from the roll load to be bent back. Moreover, certain roll bendings can be set, so as to deliberately modify the rolled material profile.
Known bending devices, which act on the roll journals or on the chucks of the roll bearings, either expand the rolls of the roll pair toward the support or intermediate rolls, or else draw the rolls toward the rolled material. The first case is referred to as positive roll bending and the second as negative roll bending.
A generic bending device is known from European Patent Application 0 768 125 A1. Here, the bending forces are conveyed via bending blocks to the bearing chucks of the rolls, which are run on pairs of cylindrical rods that are arranged in the windows of the roll stand and whose ends are connected indirectly to the roll stand. However, this known bending device has the disadvantage that only either positive or negative bending forces can be introduced to the working rolls. This has proved disadvantageous for the rolling process, especially when a change is made from positive to negative bending, in which the working rolls can elevate from the support rolls. This leads to quality losses in the rolled material.